Desulfurization process



y 1969 N- E. BLACKWELL Ill, ETAL 3,446,728

DESULFURIZATION PROCESS Sheet 2 of2 Filed Oct. 4, 1966 FIGURE 2 BATCH HEAT SOAKING TESTS BACHAQUERO TOPPED CRUDE C E V R U C CURVE D CURVE B CURVE A E O O O O O O O 8 6 5 l lOO IOOO O FEED VOL. DISTILLED N. E. BLACKWELL m w. J. METRAILER vEmoRs PATENT ATTORNEY United States Patent 3,446,728 DESULFURIZATION PROCESS Noah E. Blackwell III, and William J. Metrailer, Baton Rouge, La., assignors to Esso Research and Engineering Company, a corporation of Delaware Filed Oct. 4, 1966, Ser. No. 584,170 Int. Cl. Cg 29/16, 29/10 US. Cl. 208-218 6 Claims ABSTRACT OF THE DISCLOSURE This invention relates to an improved desulfurization process. More particularly the invention relates to an improved desulfurization process characterized by unique pretreatment steps which provide a greater quantity of gas oil for hydrodesulfurization.

Hydrodesulfurization has long been recognized as a means of removing sulfur from residual oils and other heavy petroleum fractions such as gas oils. Many techniques and many catalysts have been suggested in the literature and in patents for reducing the sulfur content of feedstocks for catalytic cracking and other petroleum refining processes and also for reducing the sulfur content of fuel oil components.

The problem which has not been solved to date is the problem of producing a fuel oil containing about l2% sulfur from a petroleum residuum containing more than 23% sulfur. Fuel oil users are unwilling to pay any significant premium for low sulfur fuel oil and thus desulfurization must be accomplished at a minimum cost. Where the gravity and sulfur content of the feedstock is not too high, vacuum distillation followed by hydrodesulfurization of the vacuum gas oil and blending of the desulfurized gas oil with the vacuum bottoms is the least expensive way of making low sulfur fuel oil. However, when the topped crude or petroleum residuum contains a large proportion of materials boiling above 1030-1100 F. vacuum distillation provides an overall sulfur reduction of only -30% which is or soon will be unsatisfactory from a sulfur reduction standpoint. It is probable that the local regulations will require a fuel oil sulfur content of 1.5% or less within the next ten years.

The object of the invention is to provide a method of making vacuum distillation applicable to high gravity, high sulfur feeds employing a minimum of pretreatment of the feeds. We have found that this object can be achieved by heat soaking the feed in the presence of a gas comprising a major amount of hydrogen and a minor amount of H S prior to vacuum distillation.

The process of the invention will be more fully described in conjunction with the drawings in which FIG- URE 1 is a diagrammatic flow sheet of a preferred embodiment of the process and FIGURE 2 is a graph showing the distillation curves of Bachaquero topped crude after heat soaking.

Referring to FIGURE 1 a petroleum crude oil is fed by line -1 to atmospheric distillation column 2 for separation of the light fractions boiling at less than 500650 F. The fractions are removed fro-m the column by lines 3, 4 and 5. This separation provides a reduced crude or petroleum residuum comprising about 5090 vol. percent of the crude oil. Suitable crude oils are those having a sulfur content of 1.0-5.5 wt. percent sulfur. These cr-udes provide atmospheric residuums containing 1.56.5 wt. percent sulfur. The process of the invention is most beneficial for oils which have a large proportion of residual components, i.e., 30-70 vol. percent of the oil boils above 700 F. The sulfur in this portion of the oil is present in the less reactive forms such as sulfides and as ring compounds such as substituted thiophenes. The oil is also characterized by metal contents of 50-1000 p.p.m. and often by a high content of coke forming hydrocarbons and nitrogenous contaminants.

The reduced crude is passed by line 6 to heat soaking vessel 7.

Heat soaking is a non-catalytic thermal treatment characterized by retention of the oil in the heat soaking vessel for an extended period of time whereby 10-50% of the 1100 F. components are converted to material boiling between 700-1100 F. Conditions are selected to avoid any substantial amount of cracking and consequent production of C -C hydrocarbons thus heat soaking is intrinsically different from short residence time treatments such as thermal cracking and v'isbreaking. Heat soaking is carried out at a temperature of 600-900 F., preferably 700850 F. and a pressure of 100-l 000 p.s.i.a. Residence times of 0.5 to 5.5 hours are used. The heat soaking step of the invention differs from conventional heat soaking in the employment of a stream of gas comprising a major amount of hydrogen and a minor amount of H 8. The gas is passed continuously through the heat soaking vessel at the rate of 400 to 2000 cu. ft. per bbl. of oil in the vessel. Heat soaking can be carried out as a batch process with two or more heat soaking drums being used on an alternating basis but preferably continuous operations are carried out in vessels internally arranged to provide the desired hold time of 0.5 to 5.5 hours. The hydrogen-H 8 gas comprises to vol. percent hydrogen and 5 to 20 vol. percent H S. The treat gas is continuously cycled through the heat soaker by lines 9, 10 and 31. When required, contaminants are removed by passing a side stream of the gas by line 30 to gas separator 11. Makeup hydrogen-H 8 mixture is supplied from the hydrodesulfurization reactor overhead by lines 19 and 31 and makeup H 8 is supplied by lines 22 and 31.

Heat soaked material is passed by line 12' to vacuum distillation column 13-. If desired, light hydrocarbons boiling below about 500 6 50 F. can be separated by a flash vessel, not shown, located in line 12. The vacuum column is operated at temperatures ranging from 550 to 700 F. and pressures ranging from 1 to mm. Hg. The cut point of the column ranges from 900--1150 F. (atmospheric equivalent temperature), providing the maximum amount of vacuum gas oil boiling in the range of 6004150, preferably 700-1100 F. for hydrodesulfurization. Vacuum distillation of atmospheric residual stock which 'has been heat soaked in the manner described yields about 6570% gas oil as compared to about 50 without heat soaking.

Vacuum gas oil is passed by line 14 to hydrodesulfurization reactor 15. Any suitable type of hydrodesulfurization reactor and a conventional catalyst are employed. Suitable hydrogenating components include mixtures of a member of the group consisting of Group VI oxides and sulfides with a member of the group consisting of iron, cobalt and nickel oxides and sulfides deposited on a porous carrier. Mixtures of the oxides and sulfides of cobalt, nickel, tungsten and molybdenum on supports containing alumina, bauxite, silica, magnesia, zirconia are preferred catalysts. Cobalt molybdate, nickel molybdate or tungsten sulfide with nickel sulfide are the most preferred metal salt combinations and alumina and silica alumina are the most preferred supports. The reaction conditions are those known for catalytic hydrodesulfurization and will ordinarily involve a temperature of 600 to 850 F., a pressure in the range of 200 to 2000 p.s.i.a., a hydrogen partial pressure of 100 to 1800 p.s.i.a., a space velocity of 0.5 to 5.0 v./v./hr., and a hydrogen to oil ratio of 500 to 5000 s.c.f. per bbl. of feed. Makeup hydrogen for desulfurization is passed by line 16 to reactor 15. Recycle hydrogen is supplied by lines 17 and 16. Unreacted hydrogen and H leave the reactor by line 18. Part of this gas mixture can be passed by line 19 to line 3 1 for use in heat soaking. The remainder of the gas mixture passes from line 18 to line 30 and thence to gas separator 11. Gas separator 11 is shown schematically and it 'may comprise one or more vessels arranged to separate hydrocarbons as liquids or gases or both and to separate hydrogen and H 8. Light hydrocarbon gases are removed from the separator by line 20. H 8 is removed from the separator by lines 21 and 23 and when required a part of the H S is passed by lines 22 and 31 to heat soaker 7 to adjust the H 5 content of the heat soaker gas. The balance of the H 5 is passed by line 23 to a sulfur recovery zone not shown. The streams of H 5, hydrogen and mixtures thereof are directed and proportioned in the system by suitable valves and instrumentation not shown.

Desulfurized gas oil is removed from reactor 15 by line 24. Preferably this oil is blended with vacuum tower bottoms from lines 25 and 2 6 to provide a low sulfur blended fuel oil. Cutter stock can be added by line 27 to adjust the viscosity of the fuel oil. If desired all or part of the desulfurized gas oil can be recovered by line 28 for use as catalytic cracking stock or hydrocracking stock. In another embodiment all or part of the vacuum bottoms can be recycled to the heat soaking zone by line 2 9.

FIGURE 2 shows plots of the vacuum distillation curves (ASTM D-1l60) for heat soaked Bachaquero topped crude. Heat soaking was carried out at 750 F. and 800 p.s.i.g. employing 1000 s.c.f. of gas per barrel of feed. The feed was on temperature for 4 hours. Curve A shows the distillation curve for feed, curve B shows the distillation curve for heat soaking with hydrogen and curves C and D show the distillation curves when the heat soaking is conducted in the presence of a gas containing H 5 and 90% hydrogen.

If it were desirable to use a cut point of 1050 F. in vacuum distillation it will be seen from FIGURE 2 that 56-58% of vacuum gas oil would be obtained for hydrodesulfurization from the feed or from heat soaking with hydrogen. In contrast at least 66% vacuum gas oil is distilled when the H Shydrogen gas is passed through the heat soaking zone. Furthermore the percentage distilled at any temperature is 1020% greater in the case of heat soaking according to the invention with the result that this material is more easily hydrodesulfurized.

The following example discloses the operation of the process.

Example The charge stock employed is a Venezuelan crude having a gravity of 26.3 API at 60 F., a sulfur content of 1.39% by weight, a metals content of 156 p.p.m. nickel by weight, and it contains 6% by Weight asphaltenes. The residuum from the crude is not a suitable stock for direct hydrodesulfurization because of its high metals and asphaltene content.

When 100 bbl. of this charge stock is topped by atmospheric distillation to produce fuel oil of 175 S.S.F. 122 F. viscosity, a yield of 65.6 bbl. with a sulfur content of 1.82% by weight is obtained. Of this 65.6 bbl. residuum, 52.4 bbl. boils above 700 F.+ and 24.0 bbl. boils above 1100 F. The material boiling between 700 F. and 1100 F. has a sulfur content of 1.36% by weight. A 700- 1100 F. heavy vacuum gas oil is prepared by vacuum d stillation without previous heat soaking. The 28.4 bbl.

of heavy vacuum gas oil so produced is subjected to bydrodesulfurization over a cobalt molybdate catalyst at 700 F., 800 p.s.i.g., and 1500 s.c.f./b. of H treat gas at a feed rate of 1.0 vol. feed per hour per vol. of catalyst. At these conditions of the sulfur present in the feed is converted to hydrogen sulfide and is separated from the product to yield a product containing 0.2% sulfur by weight in a volumetric yield of 100%. The hydrodesulfurized product is blended back with the 24.0 bbl. of 1l00 F.+ bottoms and the 13.2 bbl. lighter material (700 F.) originally present in the topped crude to produce 65.6 bbl. fuel oil with a sulfur content of 1.31% by weight. Operating in this manner it is possible to obtain an overall sulfur reduction of only 28%.

If, however, the 700 F.+ material is subjected to heat treatment in the presence of H and H 5 before vacuum distillation, an enhanced yield of vacuum gas oil is obtained. When the 700 F.+ bottoms (52.4 bbl.) is subjected to heat soaking at 800 p.s.i.g. and 750 F. for four hours holding time and in the presence of 1000 s.c.f. per hour treat gas per bbl. of oil the treatment results in conversion of about 40% of the 1100 F.+ material to material boiling within or slightly below the 700-1100" F. range and this material contains about one-third of the sulfur formerly present in the 1100 F.+ material. Thus, the feed to the hydrodesulfurization step amounts to about 38 bbl. per 100 bbl. crude and it has a sulfur content of about 1.58 by weight. The same conditions as those set forth above are employed in the desulfurization step resulting in a product heavy gas oil containing about 0.24% sulfur. Reblending in a like manner as previously described results in a final volume of 38 bbl. fuel oil per 100 bbl. crude charged and which has a sulfur content of 0.98% by weight. Overall desulfurization is 46% in comparison with the 28% achieved when the heat soaking in the presence of H and H 5 was omitted. Furthermore, the blended fuel oil contains less than 1% sulfur making it an acceptable fuel at locations where most fuel oils cannot be used.

Thus, the process of the present invention provides a means of meeting all foreseen requirements with respect to the sulfur content of industrial fuel oil. Only two uncomplicated and relatively inexpensive processing steps, e.g., heat soaking and vacuum distillation are required prior to catalytic hydrodesulfurization. The process achieves a sulfur reduction of 30-70 wt. percent based on the sulfur content of the petroleum residuum. Petroleum residuums containing l-2 wt. percent sulfur can be treated according to the invention to provide heavy fuel oil blends containing less than 1.0 wt. percent sulfur.

What is claimed is:

1. A process for the production of low sulfur fuel oil comprising the steps of:

(1) Heat soaking a sulfur-containing topped petroleum residuum fraction for 0.5 to 5.5 hours at a temperature in the range of 600 to 800 F. and a pressure of 100 to 1000 p.s.i.a. While continuously passing 400 to 2000 s.c.f. per bbl. of a gas containing 80 to vol. percent H and 5 to 20 vol. percent H 8 through the residuum in intimate contact therewith.

(2) Passing the heat soaked residuum to a vacuum distillation zone.

(3) Distilling the residuum at a temperature in the range of 550 to 700 F. and a pressure in the range of 1 to mm. Hg.

(4) Recovering a vacuum gas oil fraction and a vacuum bottoms fraction.

(5) Passing the vacuum gas oil fraction to a hydrodesulfurization zone.

(6) Contacting the vacuum gas oil with a stream of hydrogen containing gas at a temperature of 600 to 850 F. and a pressure in the range of 200 to 2000 p.s.i.a. in the presence of hydrodesulfurization catalySt.

(7) Recovering a desulfurized vacuum gas oil.

5 6 (8) Blending the desulfurized vacuum gas oil frac 6. Process according to claim 1 in which the heat soaktion with the vacuum bottoms fraction. ing step converts -10-50 wt. percent of the 1100 F.+ (9) And recovering a low sulfur fuel oil. components to material boiling between 7001100 F. 2. Process according to claim 1 in which the hydrodesulfurization catalyst comprises a mixture of a mem- 5 References Cited ber of the group consisting of Group VI oxides and UNITED STATES PATENTS sulfides with a member of the group consisting of iron, i cobalt and nickel oxides and sulfides deposited upon a 2928787 3/1960 Van Dyck Fear 208 212 3,017,345 1/1962 Eastman 208-210 pmuscamer' 3,271,302 9/1966 Gleim 20s -210 3. Process accordin to claim 2 1n WhlCh the catalyst 10 3,291,721 12/1966 Schuman comprises cobalt molybdate on alumina.

4. Process according to claim 1 in which the vacuum g on boils in the range of 700 1 100 F. DELBERT E. GANTZ, P1 "may Eaamuzer.

5. Process according to claim 1 in which the petroleum G. J. CRASANAKIS, Assistant Examiner. residuum contains 1-2 wt. percent sulfur and the fuel 15 oil contains less than 1.0 wt. percent sulfur. 

